1. Field of the Invention
present invention relates to a track maintenance machine for excavating material from a bed supporting a track including rails, which comprises a machine frame extending in a longitudinal direction and comprising an upwardly recessed machine frame section, undercarriages supporting the machine frame on the track for movement in an operating direction, and sequentially arranged on the machine frame in the operating direction, a ballast receptacle comprising means for discharging the ballast from the receptacle, an inclined, vertically adjustable and revolvable endless excavating chain having an upper end and comprising a drive at the upper end for revolving the chain, a track lifting device, and a conveying arrangement arranged to remove the received excavated material and having an inlet end arranged below the upper excavating chain end to receive the excavated material therefrom.
2. Description of the Prior Art
U.S. Pat. No. 5,553,674 discloses a ballast cleaning machine comprising a vertically adjustable endless excavating chain revolvable around the machine frame and delivering the excavated ballast to a screening arrangement for cleaning. A ballast storage car may be connected to the rear end of the ballast cleaning machine so that additional clean ballast stored in the car may be used for preparing a new ballast bed. A vertically and transversely adjustable suction pipe is arranged ahead of the excavating chain, in the operating direction, to aspirate ballast ahead of the excavating chain. In this way, a gap is created in the ballast bed to enable the transverse excavating chain strand to be inserted underneath the track.
Another track maintenance machine has been disclosed in U.S. Pat. No. 5,257,580. It serves for the excavation of material from a track bed, in conjunction with producing a protective layer on the subgrade of a track. To enable a large volume of ballast to be excavated, the revolvable excavating chain is of large dimension and its upper portion is revolved around the machine frame, for which reason the machine frame must have a section of correspondingly reduced transverse dimensions to permit the excavating chain to be revolved therearound. This increases the cost of production of the machine frame. A ballast storage receptacle is mounted on the rear end of the machine frame to enable additional ballast to be continuously delivered to the operating site while the encrusted ballast is excavated and a conveying arrangement removes the excavated ballast to a storage car preceding the machine in the operating direction. An undercarriage with four axles precedes the excavating chain in the operating direction and is displaceable in the longitudinal direction of the machine frame to enable the track to be lifted sufficiently to enable the large excavating chain to be operated without difficulty.
Finally, it is known from U.S. Pat. Nos. 4,357,874 and 4,502,389 to use a ballast excavating chain mounted underneath an upwardly recessed machine frame section in conjunction with the removal of track sections from the track. The machine frame must be longer than the track sections to be removed and the wheel base must be correspondingly wide.